Operator || cannot be applied to type bool and string / string and string

Question

Simple task that I am finding really difficult.

 Console.Write("[" + CurrentTime + "] Name a day of the week? ");
 string vDay = Console.ReadLine();
 if (vDay != "Monday" || "Tuesday" || "Wednesday" || "Thursday" || "Friday")
 {
  Console.WriteLine("that is not a valid day of the week");
 }

Firsty when I use != it gives me an error saying "cannot be applied to bool and string" without the != and just the = I get "string and string"

Basically what I am trying to do is if someone types "hello" for example it will say that is not a valid day of the week.

Such a simple task but im finding it so difficult, thanks for any help.

You could do something else entirely: List<String> validDays = new List<string> { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" }; if (!validDays.Contains(vDay)) — Johannes
– Johannes, Commented May 8, 2014 at 10:54

Science_Fiction · Accepted Answer · 2014-05-08 10:51:16Z

8

Might be cleaner to have something like:

List<string> list = new List<string> { "Monday", "Tuesday", "Wednesday", "Thursday", ... };

if (!list.Contains(vDay ))
{
    Console.WriteLine("that is not a valid day of the week");
}

answered May 8, 2014 at 10:51

Science_Fiction

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1 Comment

Abhitalks Over a year ago

This is ok. But it doesn't answer the Op's original problem of why the error says "cannot be applied to bool and string".

Antti Haapala · Accepted Answer · 2014-05-08 10:54:30Z

6

This is what you need:

if (vDay != "Monday" && vDay != "Tuesday" && vDay != "Wednesday" && vDay != "Thursday" && vDay != "Friday")
{
      Console.WriteLine("that is not a valid day of the week");
}

edited May 8, 2014 at 10:54

Antti Haapala

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answered May 8, 2014 at 10:48

Sadique

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5 Comments

Grundy Over a year ago

or check with List.Contains

hexce Over a year ago

Ah so for each one. i get it now, thank you very much :)

Abhitalks Over a year ago

@al-Acme: You may want to explain a bit to the Op, why the error says "cannot be applied to bool and string"

Antti Haapala Over a year ago

Need to use && not || here to keep the logic.

Ulugbek Umirov Over a year ago

@AnttiHaapala Indeed, otherwise it will be always true.

Abhitalks · Accepted Answer · 2014-05-08 11:04:49Z

Since all the answers here do not explain why you are facing that problem in the first place, I shall attempt to do so.

when I use != it gives me an error saying "cannot be applied to bool and string"

This is because, in your code:

...vDay != "Monday" || "Tuesday" ...

vDay is compared to string "Monday" which evaluates successfully and then the result (which is boolean) is compared to string "Tuesday". This gives you the problem of "...cannot be applied to bool and string.."

without the != and just the = I get "string and string

vDay is being assigned the value of "Monday" (which could result in string "Monday") however the string "Monday" is being compared with string "Tuesday". This gives you the problem of "...cannot be applied to string and string..".

The correct way would be to specify operators separately:

...vDay != "Monday" && vDay != "Tuesday"...

Or using the other ways as best described by other answers.

StuartLC · Accepted Answer · 2014-05-08 11:00:18Z

Here's another take, using set-based logic.

 var days = new HashSet<string> { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };
 if (!days.Contains(vDay))
 {
    Console.WriteLine("that is not a valid day of the week");
 }

Edit

I guess to explain the error:

Operator != on String accepts only a single string on the RHS of the operator, and neither does C# support List creation through the logical or || operator (if this is what was intended, nor conversely, projection of the != operator across the ||ed strings). However, a set can be created and set operations such as Contains can be used. Hashset would typically be my first choice in such a scenario, as it acts as an indexed lookup (although arguably overkill for a set of ~5 strings, this will scale much better than List or Array for much larger sets).

John Rams · Accepted Answer · 2018-06-10 07:34:52Z

0

if (vDay == "Monday" ||vDay == "Tuesday" ||vDay == "Wednesday" ||vDay == "Thursday" ||vDay == "Friday")
 {
  Console.WriteLine("is not a valid day of the week");
 }

This should do it.

answered Jun 10, 2018 at 7:34

John Rams

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Comments

Zoe - Save the data dump · Accepted Answer · 2018-08-22 17:32:45Z

-2

Text='<%# Eval("STS").ToString() == "N" ||Eval("STS").ToString() =="R"  ? "<h5>Approve?</h5>" : "<h5>Approved!</h5>"  %>'

edited Aug 22, 2018 at 17:32

Zoe - Save the data dump

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answered Aug 22, 2018 at 17:15

arup

1

1 Comment

Yunnosch Over a year ago

Can you turn this into something of a helpful answer? It is unreadable, code-only (at most) and afaict totally unrelated.

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